Daylighting methods for increasing the amount of available light within structures are well known. Conventional daylighting methods typically employ prisms or other microstructures to guide/re-direct and/or diffuse light beams of sunlight by refraction and/or reflection to increase illumination into the interior of a room uniformly while reducing glare. Daylighting constructions frequently utilize microstructures such as a series of grooves provided in films or sheets that are capable of refracting and/or reflecting incident light through the microstructures by total internal reflection (TIR).
Daylighting methods are becoming widely adopted. Daylighting increases ambient light within a building and can result in significant energy savings by reducing or eliminating the need for electric lighting during daytime hours. One disadvantage of a building without a sunlight redirecting apparatus, or daylighting film, is the inability to project light into the interior of a building. For example, if there is no apparatus, such as a reflector positioned inside or outside the window, sunlight cannot be directed to an interior space far away from the window. That is, typical, unguided sunlight will fall on the floor near the window when incident into a room. Thus, the illuminating effect is often wasted on undesired areas.
Accordingly, methods have been introduced in an attempt to overcome this disadvantage by using unique, daylighting constructions. One such method employs a light redirecting film adapted for engagement against a window. Such light redirecting films or sheets generally include a planar base and at least one light redirecting microstructure provided on the side of the sheet opposite the base. The planar base is attached to the window such that the microstructures on the opposite side face away from the window.
However, conventional attachment methods interfere with the optical properties of the microstructure, and disadvantageously degrade light projecting properties of the daylighting film. For example, conventional attachment methods put the adhesive on the planar side or base of the micro structured film, or sheet, and adhere the base to the light incident glazing to avoid degrading the optical re-directing/daylighting properties of the microstructure defining surface opposite the base. Note, that in such a conventional assembly, the daylighting microstructures generally are disposed opposite the base and face inward into the room to be illuminated. It is generally assumed that it is not possible to provide an adhesive on the light guiding microstructures without substantially degrading optical properties and thereby defeating the daylighting effect. For this reason, conventional methods of attaching daylighting microstructures to a glazing surface face the microstructures inward into a room, and avoid covering the microstructure with adhesive.
Therefore, what is needed is an attachment system for securing a daylighting sheet comprising a series of light redirecting microstructures directly to a glazing surface without degrading the light redirecting optical properties of the resulting assembly.
A further disadvantage of conventional attachment methods of a daylighting film to a glazing, such as a window surface, is the thermal expansion coefficient mismatch between the different materials comprising the glass or glazing, heated by incident light, and the adjacent planar base of the plastic daylighting sheet or film that must be covered with adhesive to a maximum extent in order to adhere to the glazing surface. Further, PSA adhesives can migrate, which means they can flow and further change the optical properties of the daylighting sheet after time has passed. Therefore, what is needed is a new way of mounting a daylighting sheet comprising a series of microstructures to a glazing surface using a PSA formulation that does not substantially migrate, and enhances optical properties, or at a minimum does not substantially degrade optical properties of the daylighting sheet
What is also needed is an attachment system that would facilitate cost effective ease of re-attachment and/or replacement of such daylighting film without damage to a glazing surface. For example, it would be desirable for an attachment method to facilitate changing position of a daylighting film to remove air bubbles or deformations without adversely affecting optical properties of the microstructures. And, such an attachment system advantageously would facilitate cost effective implementation of daylighting, thus saving energy costs for electric lighting.